Nanopore adaptive sampling to identify the NLR gene family in melon (Cucumis melo L.)

Nanopore adaptive sampling (NAS) offers a promising approach for assessing genetic diversity in targeted genomic regions. Here we designed and validated an experiment to enrich a set of resistance genes in several melon cultivars as a proof of concept.

Using the same reference to guide read acceptance or rejection with NAS, we successfully and accurately reconstructed the 15 regions in two newly assembled ssp. melo genomes and in a third ssp. agrestis cultivar. We obtained fourfold enrichment regardless of the tested samples, but with some variations according to the enriched regions. The accuracy of our assembly was further confirmed by PCR in the agrestis cultivar. We discussed parameters that could influence the enrichment and accuracy of NAS generated assemblies.

Overall, we demonstrated that NAS is a simple and efficient approach for exploring complex genomic regions, such as clusters of Nucleotide-binding site leucine-rich repeat (NLR) resistance genes. These regions are characterized by containing a high number of copy number variations, presence-absence polymorphisms and repetitive elements. These features make accurate assembly challenging but are crucial to study due to their central role in plant immunity and disease resistance. This approach facilitates resistance gene characterization in a large number of individuals, as required when breeding new cultivars suitable for the agroecological transition.